Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $23.84   10.182%   $26.2674   $26.27   $26.25   $26.30  
  Purchase #2 $214.83   11.657%   $239.8727   $239.87   $239.85   $239.90  
  Purchase #3 $158.32   8.441%   $171.6838   $171.68   $171.70   $171.70  
  Purchase #4 $13.36   7.821%   $14.4049   $14.40   $14.40   $14.40  
  Purchase #5 $231.91   5.144%   $243.8395   $243.84   $243.85   $243.80  
  Purchase #6 $177.67   4.333%   $185.3684   $185.37   $185.35   $185.40  
  Purchase #7 $42.49   11.816%   $47.5106   $47.51   $47.50   $47.50  
  7 purchase totals = $862.42       $928.9473   $928.94   $928.90   $929.00